Known vacuum heat treating furnaces employ cooling gas injection systems to rapidly cool workpieces from the heat treating temperature. The workpieces are heated in a hot zone which is enclosed by a hot zone wall that retains heat inside the hot zone. After heat treatment, cooling gas is injected into the hot zone to cool the workpieces. The cooling gas flows across the hot zone to cool the workpieces and exits through one or more exit ports in the hot zone wall. The exit ports are typically small to minimize the escape of heat from the hot zone during heat treatment.
One problem with known vacuum treating furnaces occurs when the workpiece is not cooled uniformly. In many furnaces, the stream of cooling gas contacts one part of the workpiece load more than other parts, resulting in areas that receive too little or too much cooling. When workpieces are not cooled uniformly, the finished workpiece may not exhibit the desired properties, such as hardness and ductility. Non-uniform cooling is a common problem in systems that draw cooling gas to exit ports located at only one end of the hot zone. Non-uniform cooling is also a problem in furnaces where the flow of cooling gas is fixed in one configuration that cannot be adjusted or adapted to cool workpieces having different sizes and geometries.
Directional cooling systems have been developed to improve cooling by controlling the flow of cooling gas that enters the hot zone. In directional cooling systems, injection of cooling gas can be concentrated in different sections of the hot zone to cool specific areas of the workpiece. Although directional cooling systems provide better control of cooling gas entering the hot zone, the cooling gas stream is typically discharged from one end of the hot zone. As a result, the cooling gas stream is drawn to one section of the hot zone, which still results in uneven cooling along the length of the workpiece.
Another problem with known directional cooling systems is the placement of actuators, dampers, and other moving components in the hot zone. When moving components are routinely exposed to high temperatures in the hot zone, the components become damaged over time, increasing maintenance and equipment downtime. As a result, the known vacuum heat treating furnaces and cooling systems fall short of the needs of furnace users who desire uniform cooling of workpieces and reduced maintenance of their vacuum furnaces.